Theme display in IE and Firefox

Hello! I'm building a site on Drupal 7. I'm working in  Mozilla Firefox. I tried viewing the site in IE 7. The menu buttons on the site lose their smoothness in IE 7, becoming sharp at the corners, and some blocks are slightly misaligned when displayed. The fonts change size in some places. The question arises: what needs to be done for the site to display universally as intended?  After all, there is an example, say, Yandex, which displays fine in IE 7! What’s the secret? Dmitry.